The Collaborative International Dictionary of English v.0.48:

Impure \Im*pure"\, v. t.
   To defile; to pollute. [Obs.] --Bp. Hall.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Impure \Im*pure"\, a. [L. impurus; pref. im- not + purus pure:
   cf. F. impur. See Pure.]
   [1913 Webster]
   1. Not pure; not clean; dirty; foul; filthy; containing
      something which is unclean or unwholesome; mixed or
      impregnated extraneous substances; adulterated; as, impure
      water or air; impure drugs, food, etc.
      [1913 Webster]

   2. Defiled by sin or guilt; unholy; unhallowed; -- said of
      persons or things.
      [1913 Webster]

   3. Unchaste; lewd; unclean; obscene; as, impure language or
      ideas. "Impure desires." --Cowper.
      [1913 Webster]

   4. (Script.) Not purified according to the ceremonial law of
      Moses; unclean.
      [1913 Webster]

   5. (Language) Not accurate; not idiomatic; as, impure Latin;
      an impure style.
      [1913 Webster]

WordNet (r) 3.0 (2006):

impure
    adj 1: combined with extraneous elements [ant: pure]
    2: (used of persons or behaviors) immoral or obscene; "impure
       thoughts" [ant: pure]
    3: having a physical or moral blemish so as to make impure
       according to dietary or ceremonial laws; "unclean meat"; "and
       the swine...is unclean to you"-Leviticus 11:3 [syn:
       unclean, impure] [ant: clean]

Moby Thesaurus II by Grady Ward, 1.0:

190 Moby Thesaurus words for "impure":
   Adamic, Doric, Fescennine, Rabelaisian, adulterated, alloyed,
   backsliding, barbaric, barbarous, bawdy, belowstairs, besmirched,
   black, blemished, blue, cacophonous, carnal, clumsy, coarse,
   common, contaminated, corrupted, crude, damaged, debased,
   defective, deficient, defiled, degenerate, depraved, dirty,
   dissolute, doggerel, dysphemistic, erring, erroneous, evil, fallen,
   fallible, faulty, feculent, filthy, fleshly, forbidden, foul,
   foul-mouthed, foul-spoken, foul-tongued, found wanting, frail,
   fulsome, graceless, gross, grubby, harsh, immature, immodest,
   immoral, impaired, imperfect, imprecise, improper, in bad taste,
   inaccurate, inadequate, incomplete, inconcinnate, inconcinnous,
   incorrect, indecent, indecorous, inelegant, inexact, infected,
   infelicitous, infirm, ithyphallic, lacking, lapsed, lascivious,
   lecherous, lewd, libidinous, licentious, loose, low, lubricious,
   lubricous, lurid, lustful, maculate, makeshift, mediocre, mixed,
   nasty, native, nonkosher, not perfect, obscene, of easy virtue,
   off, offensive, outlandish, partial, patchy, peccable, polluted,
   pornographic, postlapsarian, prodigal, promiscuous, prurient,
   putrescent, putrid, raunchy, raw, recidivist, recidivistic, ribald,
   ritually unclean, rotten, rude, run-of-mine, salacious, scarlet,
   scummy, scurrile, scurrilous, sensual, short, sinful, sketchy,
   smirched, smoking-room, smutty, soiled, soily, squalid, sullied,
   sultry, tainted, tasteless, tref, unangelic, unbathed, unchaste,
   unclean, uncleanly, uncourtly, uncouth, undeveloped, undignified,
   uneuphonious, uneven, unfelicitous, unfinished, ungodly, ungood,
   ungraceful, ungraded, unhallowed, unholy, unperfected, unpolished,
   unprintable, unpure, unrefined, unrepeatable, unrighteous,
   unsaintly, unscoured, unscrubbed, unseemly, unsorted, unsound,
   unswept, unthorough, unvirginal, unvirtuous, unwashed, unwiped,
   vile, virtueless, vitiated, vulgar, wanting, wanton, wayward, weak,
   wicked